Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $52.34   7.156%   $56.0855   $56.09   $56.10   $56.10  
  Purchase #2 $141.57   8.251%   $153.2509   $153.25   $153.25   $153.30  
  Purchase #3 $49.62   4.279%   $51.7432   $51.74   $51.75   $51.70  
  Purchase #4 $166.89   6.409%   $177.586   $177.59   $177.60   $177.60  
  Purchase #5 $120.86   5.327%   $127.2982   $127.30   $127.30   $127.30  
  Purchase #6 $184.68   13.206%   $209.0688   $209.07   $209.05   $209.10  
  Purchase #7 $114.38   12.810%   $129.0321   $129.03   $129.05   $129.00  
  7 purchase totals = $830.34       $904.0647   $904.07   $904.10   $904.10